The proposed study is designed to determine whether or not the secretory activity of the epinephrine and norepinephrine cells of the adrenal medulla of the cat is regulated by different neural populations in the hypothalamus and/or mesencephalon. Discrete loci in the hypothalamus and mesencephalon will be stimulated electrically with stereotaxically placed bipolar-electrodes. The entire hypothalamus and mesencephalon will be systematically explored at approximately 1mm intervals with precise histological localization of stimulus sites. Adrenal venous blood catecholamines will be differentially assayed using an automated trihydroxyindole fluorometic method. Blood pressure and other autonomic functions will also be monitored.